The broad, long-term objectives of this project are to develop knowledge concerning the primary human immunodeficiency virus (HIV) infection syndrome, the patterns of HIV spread, the interactions among HIV and other infectious agents, and to develop methods for the control of HIV. Accomplishment of these objectives will improve the ability to contain the HIV epidemic, and potentially contribute to the development of HIV vaccines by elucidating the reasons why some persons experience a mild initial response to HIV infection, associated with better long-term survival, while others experience a more severe response often associated with more rapid progression of HIV disease to AIDS and death. Specific aims thus are: (1) To determine the incidence, risk factors, clinical and immunologic associates of HIV transmission drug users (IDUs) and their sexual partners; (2) To investigate the occurrence of immuno-silent HIV infection.; (3) To investigate the prevalence, incidence and interactive effects of human T-cell lymphotropic virus (HTLV) type I and II, and hepatitis viruses on HIV disease; and (4) To develop methods needed for the design of behavioral interventions specific to subjects' knowledge and beliefs about HIV transmission. The above aims will be pursued with the context of a prospective cohort study of human immunodeficiency virus (HIV) infection among injecting drug users (IDUs) and their sexual partners. Subjects will be seen once every 6 months if HIV-seropositive; once every 6 months if HIV- seronegative and at low risk of HIV infection; and once every 3 months if HIV seronegative and at high risk of HIV. Vital statistics follow-up of all subjects in the study will be conducted annually through the National Death Index and death certificates will be obtained. Statistical analyses of survival and rates of change of immunological measures will be used to determine the relationship of various cofactors to progression of HIV disease. An embedded case-control study will investigate the symptoms, viral and immunological correlates of different responses of initial HIV infection.